294 W. J. Miller — Ice Movement and Erosion. 



tion should be made of the great number of large, more or less 

 jointed, to somewhat rounded and fresh erratics of Precambrian 

 rock material strewn over much of the region, especially the 

 central portion of the Remsen quadrangle. It is very com- 

 mon to find erratics ranging from five to twenty feet in diame- 

 ter, one at least measuring seventeen feet high and twenty- 

 seven feet across. The larger ones are mostly of the hard, 

 homogeneous syenite or granite. Probably the greatest amount 

 of ice erosion of the Precambrians occurred along Black river 

 between Lyons Falls and Lowville ; but this matter will be 

 referred to below. 



2. Erosion of the Sedimentaries. 



Turning our attention to the sedimentary rocks, we find that 

 ice erosion was much more effective upon them. In fact, the 

 writer believes that in the Black river valley we have one of 

 the best examples of ice erosion in northern New York. One 

 factor favoring the ice work here was the comparative softness 

 and the highly jointed character of the rocks, while another 

 factor was their ^position with reference to the ice current (see 

 below). The writer has found no sign of considerable ice ero- 

 sion in the southern part of the region here described. 



Fig. 2. 



Fig. 2. Section across the Port Leyden quadrangle two and one-half 

 miles north of Lyons Falls. Vertical scale 8*8 times the horizontal scale. 



The accompanying figure shows the profile and the geologic 

 structure across the Black river valley two and one-half miles 

 north of Lyons Falls. One of the striking features is the ter- 

 raced character of the sedimentaries, particularly from Port 

 Leyden northward. (See topographic map.) Along the river 

 course there is a slight notch in the Precambrians and just west 

 of this, on the northern part of the Port Leyden sheet, there is 



